Photon pairs with coherence time exceeding 1  μs

Zhao, Luwei; Guo, Xianxin; Liu, Chang; Sun, Yuan; Loy, M. M. T.; Du, Shengwang

doi:10.1364/optica.1.000084

Cited by 72 publications

(70 citation statements)

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“…With a cold atomic ensemble as the nonlinear medium, the dephasing rate of χ ð3Þ is comparable to the atomic natural linewidth [29][30][31][32][33][34]. In particular, the biphotons generated from spontaneous fourwave mixing (SFWM) in cold atomic ensembles have a coherence time exceeding 1 μs [35,36] with the electromagnetically induced transparency (EIT) effect [37]. The EIT slow light effect reduces the group velocity of the signal photons and, hence, extends the coherence time to 100 ns or more.…”

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confidence: 99%

Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles

Qian

Cao

et al. 2016

Phys. Rev. Lett.

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The temporal purity of single photons is crucial to the indistinguishability of independent photon sources for the fundamental study of the quantum nature of light and the development of photonic technologies. Currently, the technique for single photons heralded from time-frequency entangled biphotons created in nonlinear crystals does not guarantee the temporal-quantum purity, except using spectral filtering. Nevertheless, an entirely different situation is anticipated for narrow-band biphotons with a coherence time far longer than the time resolution of a single-photon detector. Here we demonstrate temporally pure single photons with a coherence time of 100 ns, directly heralded from the time-frequency entangled biphotons generated by spontaneous four-wave mixing in cold atomic ensembles, without any supplemented filters or cavities. A near-perfect purity and indistinguishability are both verified through Hong-Ou-Mandel quantum interference using single photons from two independent cold atomic ensembles. The time-frequency entanglement provides a route to manipulate the pure temporal state of the single-photon source. DOI: 10.1103/PhysRevLett.117.013602 The purity of the quantum state of a single photon is a prerequisite of its indistinguishability with single photons from other independent sources, and the latter is an essential basis for the realization of a scalable quantum network with distant and independent nodes [1][2][3][4][5]. Furthermore, the temporal purity of a single photon is crucial to the development of photonic technologies for quantum information science [6,7]. The traditional method to produce indistinguishable single photons is heralding time-frequency entangled biphotons generated from spontaneous parametric down-conversion (SPDC) in a nonlinear crystal which is pumped by ultrashort pulses [4,5,8]. In recent decades many new physical systems have been developed [9-13] to obtain pure single photons without time-frequency entanglement built in.In the community of quantum communication, SPDC in χ ð2Þ nonlinear media is still the preferable way to produce entangled biphotons because of its simplicity in the operation and the potential for on-chip integration and scaling up [14][15][16]. However, the intrinsic feasible phase matching condition of SPDC crystal allows an extremely broad range of temporal modes. Therefore, the typical temporal coherence time of the photon source is of femtosecond scale. Compared to the time response of most commercial single-photon detectors, which is about 1 ns, this temporal coherence time is so short that the trigger photon of the heralded single photon is measured with a large time uncertainty. This time uncertainty damages the temporal quantum purity of the single-photon source. To circumvent the time uncertainty problem due to the slowness of the detectors, a common practice is to use external spectral filtering including passive filtering with narrowband filters [4,5,17] and active filtering with an optical cavity [18]. In this case, the temporal state o...

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confidence: 99%

Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles

Qian

Cao

et al. 2016

Phys. Rev. Lett.

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“…Therefore, if the pump field is spatially modulated along the longitudinal direction of the biphoton generation, this spatial modulation will affect the biphoton temporal waveform. This effect was first reported in a recent experiment for achieving the two-photon coherence time up to about 2 µs [25]. In this experiment, the transverse Gaussian amplitude profile of the pump laser beam is projected to the biphoton longitudinal direction and revealed in the two-photon correlation function.…”

Section: ) Shaping Biphoton Temporal Waveforms With Spatially Modulamentioning

confidence: 62%

“…[25] In Ref. [25], the pump-coupling laser beams are aligned with am angle of 2.8 o to the biphoton longitudinal z-axis and the pump beam transverse Gaussian profile is projected to the z-axis. Taking into account the pump field profile effect, we modify Eq.…”

Section: ) Shaping Biphoton Temporal Waveforms With Spatially Modulamentioning

confidence: 99%

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Narrowband Biphotons: Generation, Manipulation, and Applications

Chuu

2015

Engineering the Atom-Photon Interaction

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In this chapter, we review recent advances in generating narrowband biphotons with long coherence time using spontaneous parametric interaction in monolithic cavity with cluster effect as well as in cold atoms with electromagnetically induced transparency. Engineering and manipulating the temporal waveforms of these long biphotons provide efficient means for controlling light-matter quantum interaction at the single-photon level. We also review recent experiments using temporally long biphotons and single photons.

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“…A continuous spontaneous four-wave mixing (SFWM) process in a cold-atom cloud can produce non-classical paired photons with sub-natural linewidth, determined by the transmission window caused by electromagnetically induced transparency (EIT) [13][14][15][16][17][18] . Especially with high optical depths, SFWM in an atomic ensemble can produce photon pairs with higher generation rates and longer temporal coherence [19,20] . When the pump beams in the SFWM are in the continuous mode, the atomic ensembles are always emitting photons from spontaneous Raman emission process.…”

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confidence: 99%

Interfering single photons retreived from collective atomic excitations in two dense cold-atom clouds

Cao

Wen

et al. 2016

中国光学快报

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We report the Hong-Ou-Mandel (HOM) interference, with visibility of 91%, produced from two independent single photons retrieved from collective atomic excitations in two separate cold-atom clouds with high optical depths of 90. The high visibility of the HOM dip is ascribed to the pure single photon in the Fock state that was generated from a dense-cold-atom cloud pumping by a short pulse. The visibility is always the same regardless of the time response of the single-photon detectors. This result experimentally shows that the single photons retrieved are in a separable temporal state with their idler photons.OCIS codes: 020. 4180, 190.4223, 020.3320, 270.5565. doi: 10.3788/COL201614.080201.The perfect destructive two-photon interference, first observed by Hong, Ou, and Mandel (HOM) with paired photons generated from spontaneous parametric down conversion (SPDC) in χð2Þ non-linear crystal media [1] , is one of the most well-known phenomena revealing the quantum nature of photons. HOM interference of independent single photons from separate sources is the basis of quantum swapping [2,3] and hence realistic linear optical realization of quantum repeaters [4,5] . To have complete destructive interference, each of the two independent photons must be in a pure single-photon Fock state, and they must be indistinguishable in every aspect, including polarization and spatial and spectral modes. Interfering with the single photons generated from the SPDC process in non-linear crystals has been experimentally demonstrated [6][7][8] . The single photons are constituted from the signal photons heralded by the correlated idler photons. In fact, two-photon interference from independent SPDC crystals is widely used in experimental demonstration of quantum swapping [9] , multiphoton entanglement, etc. [10] , because of the high generation rate of SPDC photon pairs.However, SPDC schemes produce broadband photon pairs, typically with terahertz of linewidths and hence femtoseconds of coherence time. This implies a very strict synchronization between two independent SPDC processes, with which the temporal wave functions of two independent photons overlap in time at the beam splitter (BS). Passive spectral filtering can increase the coherence time, but waste a great amount of photons and thus seriously lower the generation rate. Active filtering through putting the SPDC crystal into a cavity is an efficient approach, but complicated cavity stabilization limits its further application [11,12] . With laser cooling and trapping technology developing fast, cold-atom clouds have become a new non-linear media to generate photon pairs and herald single photons. A continuous spontaneous four-wave mixing (SFWM) process in a cold-atom cloud can produce non-classical paired photons with sub-natural linewidth, determined by the transmission window caused by electromagnetically induced transparency (EIT) [13][14][15][16][17][18] . Especially with high optical depths, SFWM in an atomic ensemble can produce photon pairs with higher generation rate...

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Photon pairs with coherence time exceeding 1 μs

Cited by 72 publications

References 28 publications

Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles

Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles

Narrowband Biphotons: Generation, Manipulation, and Applications

Interfering single photons retreived from collective atomic excitations in two dense cold-atom clouds

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